Arc discharge synthesis of carbon nanoparticles: impacts of pressure on morphology and performance in nanofluids for direct absorption solar collectors

Direct absorption solar collectors represent a promising direction for the green processing of light energy into heat, where nanofluids play a crucial role. The properties of the nanofluid are strongly dependent on the characteristics of the nanoparticles dispersed in the base liquid. Furthermore, both the morphology and composition of the nanoparticles are significantly influenced by the method of their production. This study examines the effects of arc-discharge synthesis of carbon nanoparticles on their morphology and composition, as well as on the optical properties, viscosity, and thermal conductivity of the resulting nanofluids. Numerical modeling indicated that helium pressure in the reactor chamber influences the spatial distribution of gas temperature and carbon concentration in nanoparticle formation zones, making pressure a key factor in synthesis control. Experimental studies provided novel insights into how reactor pressure influences the morphology and composition of the nanoparticles. In turn, these synthesized carbon nanoparticles proved effective in nanofluids for direct absorption solar collectors. Comprehensive studies revealed that nanoparticle dispersibility in water and nanofluid stability rely heavily on the presence of C=O and C–O–H bonds on their surfaces. The research demonstrated that carbon nanoparticles maintain effective thermal conductivity and viscosity in nanofluids, which are crucial for solar collector applications. Additionally, optical studies indicated that the high specific surface area and conjugated graphitized structure of carbon nanoparticles enhance photothermal energy conversion, enabling more efficient solar collector designs with smaller geometric dimensions.